BACTERIAL REDUCTIONS 103 





only lack of constancy, but also conditions do not oscillate about a mean value. In 

 muscle although in periods of rest and activity there are ciianges, conditions are 

 always reverting to a comparatively steady state. The initial problem of a bacterium 

 inoculated into fresh medium is to make conditions suitable for its metabolism. In a 

 highly oxidised medium such radicals as SH groups may be unable to remain reduced 

 so that enzymes activated by SH cannot function. Yet some of the initial reactions 

 in the glycolytic chain are just the ones which require reducing conditions. The 

 enzyme systems such as those of cytochrome which tnrive under oxygenated condi- 

 tions are those which come near the end of metabohc breakdown chains. The volume 

 of culture medium compared with that of the inoculum of bacteria is enormous. Yet 

 the electrode potential soon begins to fall ; the oxygen dissolved in the medium is 

 utilised by the organisms, any oxidation-reduction systems present in the medium are 

 reduced as the potential falls to the level at which their equihbrium potential lies. 

 How are these constituents of the medium reduced ? The less likely view is thatn 

 bacteria eject a stream of reducing agent hke squids squirting out sepia. The aspect ^ 

 in harmony with the metabohc cycles described in previous pages is that bacteria 

 require energy for their rapid growth and metabolic processes and the most efficient 

 methods of getting energy are by oxidising food materials. Oxidation or dehydro- 

 genation, however, comes to a standstill unless there are hydrogen acceptors present, 

 and there is no blood stream to bring fresh supplies of oxygenated haemoglobin. Once 

 growth is established in a bacterial culture, therefore, oxygen donators and hydrogen 

 acceptors must be seized upon avidly by the cells for their metabolism and the culture 

 medium which started by having a high electrode potential will soon develop a low 

 reducing potential as more and more hydrogen acceptors will have accepted all the 

 hydrogen they can accept. The level to which the potential fall depends, of course, 

 upon the enzyme systems possessed by the bacterium studied. The electrode 

 potential reached will be governed by what hydrogen acceptors are reduced and this 

 in turn depends upon the enzymes that are present and able to function. 



So the electrode potential indicates the state of the dynamic equilibrium of the 

 culture, between the activity of the cellular enzymes and the constituents of the 

 medium. As would be expected Yudkin (1935) found that protecting the electrode 

 from contact with the bacteria made no great difference to the electrode potential. 

 It is the effects produced by the bacteria and not contact with the cells themselves 

 that affects the potential. 



The question is sometimes asked : why are intense reducing conditions developed 

 in many bacterial cultures, and why not intense oxidising conditions or a high oxida- 

 tion-reduction potential ? The answer lies in the great difference between conditions 

 of bacterial growth and those of cells in multicellular animals — it lies in the constantly 

 changing conditions of bacterial growth. At the outset, when freshly sub-cultured, the 

 bacterium is in a medium which tends to be too oxidising for active growth to start 

 (i.e., for enzymes in the initial stages of metaboHsm to be activated) and hence one of 

 the reasons for the bacterial lag phase of gro^vth. In the later stages of growth, when 

 oxidising conditions would help metabolic processes, there is an oxygen deficit, and 

 for the purpose of finding hydrogen acceptors every constituent possible in the 

 culture medium is reduced. Then as bacterial enzymic activity wanes after the 

 logarithmic phase of growth air slowly diffuses into the culture and the electrode 

 potential drifts upwards again. 



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